TOW Ross and Rachel Take a Break + TOW The Morning After, I was crying pretty much nonstop throughout the entire episode. Especially when they show the other 4 crying in Monica's bedroom. And when Rachel tells Ross that he's just changed everything forever.
The One Hundredth, when Phoebe's rocking her babies and crying.
TOW All the Haste, when Rachel finds out that Ross and Emily are going to get married.
TOW The Proposal Part 2, when Monica and Chandler propose to each other.
TOW Rachel's Date, when Rachel sees Ross and Mona together.
TOW Rachel Has a Baby, when Phoebe and Ross are talking, while looking at Emma.
TOW Monica Sings, when Ross and Rachel argue, and Rachel ends up moving out.
TOW Ross is Fine, when Joey and Ross are talking.
TOW Phoebe's Wedding, when Phoebe's saying her vows.
TOW Rachel's Going Away Party, I CANNOT watch this episode! It gets me every single time.
And of course, last but definitely not least, The Last One, with the foosball table, and all the airport scenes, and the final scene in Monica and Chandler's apartment, and of course, when Rachel shows up at Ross's apartment.
And I'm sure there were more that I'm forgetting now...